Field
Object of the invention is a hammering and rotatable drill bit belonging to a drilling device and meant for ground and rock drilling through a hollow shaft of which bit flushing air is directed to the drilling surface to the front of the drill bit and further from it towards the outer edge of the drill bit.
Description of the Related Art;
Dill bits according to the above presented preamble are previously known for example from a Finnish patent application no. 20120269 in which flushing air is directed towards the centre of the drill bit and the flushing flow is turned to the side inside the drill bit from which location it continues along the duct which is located inside the drill bit till the duct opens to be a groove, which leads towards the outer edge of the drill bit on the surface of the drill bit.
In the above described publication a drill bit is presented with the structure of which drill bit one aims to prevent the strong flushing flow from hitting the drilling surface when soft ground is being drilled. The flushing flow is directed towards the edge of the drill bit being fully turned in a sideways direction and when it has reached the surface of the drill bit it is still directed in a groove on the surface of the drill bit. This kind of flushing flow is capable of transferring the soft ground away from the drilling surface when the drill bit rotates and there is enough flow in the grooves of the drill bit which flow is not directed towards the surface to be drilled but towards the outer edge of the drill bit. In this solution the midarea of the drill bit will have a weak structure because inside the drill bit the flushing duct, which is directed to the front, must be arranged very close to the front surface of the drill bit and the ducts that are directed to the side from it are also located very close to front surface of the drill bit covering the distance when they are inside the bit crown. In the above mentioned implementation the mid-area of the drill bit also gets very little flushing because all the flushing air is directed in the direction of the radius of the crown along the drilled holes to the edges of the crown.